Microarrays were used to measure gene expression through the cell cycle of S. pombe (fission yeast), and 750 cell cycle regulated genes were identified. These were placed into clusters. Tentative assignments of transcription factors were made to the major clusters. Here, we will explore the circuitry of the S. pombe cell cycle transcriptional network. We will define how each major cluster of genes expressed in mitosis is controlled, and how the clusters are co-ordinated with one another. We will find out how four major cell cycle transcription factors, MBF, Forkhead, Prz1, and Ace2, work, and how they are controlled. We will begin to examine combinatorial control by these transcription factors. Relevance: S. pombe is an excellent choice for the kind of comprehensive and global analysis proposed here. It has been and continues to be a major tool for study of the eukaryotic cell cycle and therefore will provide further insights for understanding human cell cycle regulation and how that program is altered in disease and oncogenesis.